With demand for digital label printing rising, inks will play a pivotal role in the technology’s success. New digital ink developments will help labels shine on the shelf, thus leading to greater adoption in the future.
Printers require greater speeds and quality, all while limiting costs. Therefore, the onus is on suppliers to develop cutting-edge technologies, all while adhering to the latest legislation and requirements.
“Going back to the early days of inkjet–before 2000–it was all about getting the ink and printhead to work together reliably so that OEMs could build some hardware around the printhead,” says Phil Jackman, global product manager, digital, Sun Chemical. “Today’s ink must run in faster systems, print with smaller droplets, reliably, work in high frequency printheads, work with different printhead materials, be compatible with new media types, and the list goes on. So, inks have changed a lot in composition, and they are produced to ever higher specifications and tighter tolerances.”
“There have been many advances in recent years,” explains Renee Schouten, director of marketing for INX International Ink Co. “INX has experienced more demand from various segments, including labels and packaging. UV inks, specifically, have matured and kept pace with the advancements in printhead technology. UV inks now cure at faster rates so they can keep up with the print speeds of the latest generations of printheads. This really has helped with the overall acceptance of digital in the label and narrow web market, where conventional presses print at very high rates.”
The evolution of digital labeling printing has not coincidentally occurred in tandem with ink development. The inks must help produce a wide variety of applications, especially as short-runs are required to handle multiple SKUs.
“There is an increase of application-driven ink formulation, as the market for digital printing is highly diverse, with multiple application areas requiring specific ink characteristics,” says Matthieu Carni, director, Business Unit Inkjet at Siegwerk. “Besides, CMYK inks are not enough anymore. There is a high demand for opaque white and hexachrome printing for an extended color gamut. We also notice an increasing demand for inkjet varnish solutions to bring a digital touch to the finishing processes.”
Not all inks are created equally, either. Inks used for flexographic printing come with different attributes than their digital counterparts. For example, digital printing is typically done in a non-contact manner. “In inkjet printing, this requires the low viscosity ink to be jetted onto the surface through very small nozzles,” says Jackman. “The jetting requirement demands inks specially formulated to the unique requirements of each printhead manufacturer. Inkjet inks require more processing than flexo inks and are manufactured to tighter tolerances to ensure that they are reliable in use. Additional to jetting reliability, chemistry and substrate compatibility issues need to be addressed. Image quality and controlled drop spread need to be achieved, as well as adhesion and other physical properties onto a variety of substrates.”
There are other differences, as well. “In UV, for example, inkjet results in an ink layer that is thicker than flexo,” states Mike Pruitt, senior product manager industrial markets at Epson America. “There are ongoing developments that make the inkjet layer thinner and more uniform. General physics differ for pushing ink through a nozzle versus applying the ink via cavities on a flexible plate. However, UV flexo ink comes with a lower cost than UV digital ink.”
“Flexo inks and inkjet inks differ mainly in their viscosity,” says Lode Deprez, VP of technology, Digital, at Xeikon. “In order to ensure reliable high-frequency jetting, inkjet inks must have a low viscosity, which for UV-curable inkjet inks is about six times lower than that of commonly used UV-curable flexo inks.”
Plus, inkjet pigment particles should remain equally dispersed as the ink passes through the printhead and never block any nozzles. Inkjet ink production requires extra steps and takes much longer than flexo ink production, adds Deprez.
The pricing for digital inks has generally not been an inhibitor, though. “As one might expect, the market is becoming more mature,” says Schouten. “As with any market, the more mature and with more volume, you enjoy economies of scale. Digital ink prices have dropped. We expect to see that trend to continue with more penetration.”
The industry has faced challenges regarding raw material shortages, which is worth keeping an eye on in the future. In addition to the raw material challenge, different monomers and photoinitiators required for UV inks have seen shortages, as well. Increasing regulatory pressures on UV raw materials have also affected UV ink development.
“In the future, I believe more development is needed in water-based inks so they can be deployed in faster systems,” adds Pruitt. “Water-based inks are the safest and provide the widest gamut possible.”
Evolution of digital inks
Ink suppliers have long been developing solutions to curb VOC emissions. UV-curable inks have emerged as a suitable alternative to solvent-based technologies, as the former can perform across a wide range of substrates.
Digital ink chemistry has improved too. Where inks once featured mainly conventional UV curing, they have been optimized to handle LED-curable ink systems at the same printing speeds. Further developments in monomer chemistry and advancements in photoinitiator technology have promoted better migration with low migration UV inkjet inks, specifically as it pertains to food applications.
“Current digital printing inks offer fast curing and work at high printing speeds,” says Siegwerk’s Carni. “Due to unique photoinitiator combinations, speeds of more than 100 m/m are easily possible today. Besides, advanced monomer chemistry with a high degree of cross-linking leads to high resistance of the cured ink films while enabling the specific formulation of low migration UV inks for digital printing.”
“The proliferation of digital printing has been huge for ink development,” notes INX’s Schouten. “As soon as we develop a product for one market, there is demand from another. The labels and packaging space is a great example. We introduce a new ink and then the questions follow: can you do this? Most times we can, and that’s why the market for digital print has expanded. It’s already established for the label market, but by 2022, digital packaging for all types - from folding carton and corrugated to thin film and laminated bags and pouches, which require very different ink chemistries – is expected to exceed $22 billion annually.”
According to Schouten, modern-day digital inks can be customized for various surfaces and treatments. “This is where industrial printing is seeing a huge leap in popularity,” she says. “Substrates that were impossible to print on several years ago because of their surface geometry and material are now perfect candidates for digital printing.”
Carni says that, ultimately, digital inks will need to continue on their current path. They must further improve in terms of printability at higher run speeds while offering an even more robust low migration performance, as well as a broader color gamut.
For Xeikon, UV inkjet prices will need to come down to be more competitive with analog inks. “The production cost (milling of pigment) remains difficult to further optimize so less photoinitiators will help in doing this,” notes Deprez. “Nitrogen blankets are going to be used more intensively. E-beam also will be an option on condition the electron guns are becoming cheaper and the possible deterioration of the substrate can be minimized. Both ways also will probably help to make the ink more suitable for critical applications like food packaging, but even then always will remain less safe compared to dry toner EP.”
EP vs. inkjet
Inkjet and electrophotography (EP) are inherently different print processes. “In inkjet, liquid inks are ejected in a controlled manner from printheads onto the substrate,” explains Sun Chemical’s Jackman. “Whereas EP is an imaging technique that uses toner (powder or liquid) that is attracted electrostatically to a light induced image on a drum. This toner is then transferred physically onto the substrate or onto an intermediate transfer blanket, with subsequent transfer to the substrate before being thermally fused with heat.”
Unlike most digital print providers, Xeikon offers technologies from both ends of the spectrum. Its newly-launched Panther line covers the inkjet side of the market, complementing the company’s well-established dry toner technology.
“Since digital printing requires low viscosity, high reactivity, safe handling and very stable pigment dispersions, this has pushed the formulating chemists into new chemicals and methods of composing inks that have reached new heights in terms of chemical creativity and building blocks,” explains Deprez. “The inks are kept at high temperatures (35-50°C) in the printhead to guarantee the desired viscosity value, resulting in working toward the edge with respect to the stability of the chemistry.”
Xeikon’s PantherCure UV inks have been fine-tuned to ensure optimal performance on-press. These inks offer aesthetic and functional benefits, making them suitable for a host of label applications, ranging from health and beauty, chemicals, and the durables industry. As Xeikon’s Deprez notes, however, UV-curable inkjet inks have a lot of benefits, they also have limitations in food applications.
Meanwhile, in designing and developing its dry-ink toners, Xeikon has taken great care in choosing ingredients that deliver the best performance and results possible while meeting the most stringent requirements in terms of recyclability, absence of harmful substances, and human and environmental safety.
As Epson’s Pruitt notes, inkjet can accomodate a wider variety of inks compared to EP. Typical inkjet printing can use water-based, UV and eco-solvent inks, while EP is limited to ink specific to that system. Inkjet inks can typically handle off-the-shelf flexo media, while EP requires a primer.
“EP inks are designed as per printing technology and cannot be customized for the final application,” notes Siegwerk’s Carni. “UV inkjet inks, on the other hand, can be fully customized to concretely answer performance and compliance challenges of the individual application.”
Industry suppliers have launched multiple new solutions, many of which are being featured at Labelexpo Europe 2019.
Epson inks cover the gamut. Epson’s water-resin ink has been noted for its ability to work with a wide range of materials and its ink safety. Epson UV ink is tuned to the Epson LED curing systems and Epson printheads, which result in thinner ink and precise drop placement. All Epson ink is Good Manufacturing Practice (GMP) compliant and is manufactured under hygienic control, as well.
INX has unveiled new products designed to meet a plethora of demands. The company has developed new digital ink chemistries for multiple applications, including low odor/low migration UV inks, EB (Electron Beam) inks for indirect and secondary food contact. The inks have even been enhanced to adhere to metal packages and substrates.
“INX has what I consider to be the No. 1 R&D department in the entire industry,” says INX’s Schouten. “Our chemists develop solutions ahead of the curve, and our customers are always pushing us for the next big thing. It’s one reason why we are continually improving our ink delivery systems, so we can accommodate new fluids that previously were not jettable.”
INX has also designed ink systems, such as the new INXhrc, that are natural based and bio-renewable. INXhrc, for example, is designed to lower the CO2 carbon footprint by 25-30%.
Siegwerk tailors its solutions to meet the customer’s individual needs. Each market might require a different ink formulation, and Siegwerk has created multiple ink sets to match various applications. Siegwerk’s inks have been optimized for a host of challenging applications, including those in the food, pharma and hygiene packaging industries.
“For us, customization goes beyond classical color matching,” says Siegwerk’s Carni “It also covers optimization of adhesion, mechanical and chemical resistance, as well as assessment of migration risk. As a global leader in providing product safety, we have a team exclusively dedicated to safety regarding both regulatory compliance and brand owner requirements to ensure that our products are safe for the customer’s end use applications.”
Sun Chemical has crafted EtiJet inks for the label and narrow web space. Sun Chemical offers a portfolio of award-winning, energy-curable products for use with UV, LED and electronic beam curing technologies, as well as migration-compliant solutions for food packaging.
“Recent developments for food packaging feature SunChemical’s Amphora water-based inkjet inks that are often used in combination with the interventions of analog applied primers, adhesives, coatings and varnishes,” says Sun Chemical’s Jackman. “Aqueous formulations have a good health and safety profile and are well suited to food packaging applications.”
The company’s recent Aquacure water-based inkjet ink technology offers functionality that digital printers have wanted from water-based technology and will have a positive impact on both well established and emerging inkjet market segments, says Jackman. Aquacure technology delivers adhesion to a broad range of media, offers excellent flexibility, is odor-free and has an extensive color gamut.
Particularly relevant with digital printing, Sun Chemical has aligned its conventional coatings business with those of inkjet to provide a variety of packages to meet the emerging needs of digital print. The company has launched the SunEvo range of digital coatings for flexible packaging, labels and narrow web folding carton and corrugated.
“Sun Chemical’s R&D team is always working to advance its current inkjet technology to higher and better levels that best meets the future needs of our customers,” adds Jackman. “The digital value proposition continues to gain momentum as run lengths in many conventional print markets reduce.”
Over the years, Xeikon’s market-driven research has ensured that its toner has been continually improved to meet its customers’ requirements. According to Deprez, Xeikon’s dry toner offers excellent lightfastness, one-pass opaque white and consistent quality, all while working on a multitude of substrates. The company’s dry toner has been food approved, is odorless and offers guaranteed recyclability.
From an inkjet standpoint, the company’s PantherCure pigment-based UV-curable inks have been formulated to make the most of the Kyocera printheads. These inks are available in the four process colors (cyan, magenta, yellow, black) and in white.
“PantherCure UV inks are optimized for use without intermediate pinning,” says Deprez. “We only use pinning when laying a white foundation: A low-power LED UV source partially cures the white layer, which provides complete control over the four process colors in the layer printed on top of the white foundation. Because PantherCure UV inks do not require intermediate pinning, prints will shine with a uniform gloss, even when color densities vary, resulting in smooth images.”